The invention relates to a method for targeted reaction in the event of a contact between a machine element of a machine and an object.
Furthermore, the invention relates to a control device having a program memory, in which a computer program is stored which contains code sections with which, when the computer program is called up by the control device, the abovementioned method can be implemented.
In machines such as machine tools, production machines and/or robots, for example, a high degree of process accuracy is required in addition to high machining speeds and machining accuracy. A possible process fault represents a collision between a machine element, which may be present, for example, in the form of a tool or a spindle, and an object, which may be present, for example, in the form of a workpiece, a tool carriage or a tensioning apparatus. In comparison with other process faults, collisions result in the highest repair costs and the longest downtimes.
In order to avoid or at least reduce costs for repair work and downtimes, until now various systems and strategies have been developed. Commercially available mechanically operating apparatuses or systems with sensors have the disadvantage that they only become effective once a contact has been made and after an additional delay until the force has built up in the mechanical structure, with the result that it is then only possible to reduce the damage. Passive mechanical systems such as overload couplings, for example, are based on the principle that, in the event of excessive feed forces owing to, for example, sliding or latching couplings, the forces occurring are limited. The consequences of a collision in the case of rapid displacement movements can only be limited, however. One disadvantage here is the fact that, owing to the late reaction, generally significant damage results, in particular loss of manufacturing accuracy, since there is only a response when there has been considerable overloading of the components, i.e. if the force occurring is already high and is generally already causing damage. Furthermore, even in the case of very low displacement speeds, after a collision the balancing of the spindle and the tool also needs to be checked and, in an extreme case, the machine needs to be recalibrated, which requires considerable complexity.
If, as is often conventional practice, the drive torque of a drive of a machine axle to be displaced is evaluated, the response may likewise only be later since the collision is only identified if a high drive force has already been built up.
Using control-related solutions a series of collisions can be identified in advance and prevented. Collisions owing to the failure of control components can be ruled out owing to so-called safety functions in the numerical controller of the machine. The numerical controller can monitor protection zones, for example around clamping jaws and tailstock or boundary contours. The commercially available solutions are, however, often limited, for example often only the tip of an active tool is monitored and only simple geometries can be defined as protection zones. A further disadvantage is the fact that the workpiece is generally not taken into consideration. Owing to simulation of the NC program, collisions, for example between a workpiece or a tool, can be identified. In this case, the simulation functions with assumed tool and workpiece dimensions, with the result that loading with an incorrect workpiece (incorrect estimation of the dimensions by the eye, castings not removed) and incorrect tools cannot be identified. Errors when setting up a program can likewise not be identified.